1. override
void redepthChildren()

Adjust the depth of this node's children, if any.

Override this method in subclasses with child nodes to call redepthChild for each child. Do not call this method directly.

Source 

@override
void redepthChildren() {
  ChildType child = _firstChild;
  while (child != null) {
    redepthChild(child);
    final ParentDataType childParentData = child.parentData;
    child = childParentData.nextSibling;
  }
}